2The Experimental Method As mentioned before, correlation does not always indicate causationThe method that researchers use to answer questions about cause and effect is the experimentIn an experiment, participants receive what is called a treatment, such as a change in room temperature or a new drugResearchers carefully observe participants to see what changes may have occurred (if any)
3Limitations of the Experimental Method There are several limitations of the experimental methodThe conditions created in an experiment may not reflect conditions in real lifeExperiments must simplify conditions to yield information about cause and effectNevertheless, despite these limitations, experiments do yield useful and helpful information
4This person doesn’t normally walk around with wires on his head, and experiments may not always be able to replicate real life situations very well, but they do offer advantages with finding cause and effect
5Independent and Dependent Variables Experiments contain variables, which are factors that can vary, or changeThe independent variable is the factor that researchers manipulate to observe its effectIf researchers want to see the effect of amount of sleep on people's ability to drive through a maze, the independent variable is the amount of sleep, which researchers manipulate to see the effectThe dependent variable depends on the independent variableIn this case, the people’s ability to drive through the maze is the dependent variable, as it depends on the amount of sleep people get
6Independent and dependent variables can be recorded on a table, and displayed on an x-y axis
7Experimental and Control Groups Controlled experiments are the most informative kind of experiments, in that they use experimental and control groupsMembers of the experimental group receive the treatmentMembers of the control group do notResearchers try to make sure all other conditions are the same for both groupsThis way, researchers can conclude that the experiment’s results are caused by the treatment, not by something elseParticipants are randomly assigned to each group, and they do not know which group they are in
8Control groups allow us to see the effects of a treatment with everything else being equal What conclusion could we draw regarding the treatment given to bring the levels of creatine phosphokinase into the normal range?
10The Placebo EffectOur expectations affect how we feel or what happens to usA placebo is a substance or treatment that has no effect other than the person’s belief in itA person may believe that taking a pill will get rid of a headache, and in taking a sugar pill with no medicine, begin to feel betterResearchers should be aware of this effect when conducting experiments– just the fact of someone coming to an experiment will have an effect on that person
11Here’s an interesting article about the placebo effect Here’s an interesting article about the placebo effect. Why do you think placebos work?
12Single-Blind StudiesTo counteract expectations and the placebo effect, researchers may not tell participants what kind of treatment they are receivingBecause participants are unaware (or blind) if they are in a control or in an experimental group, it is called a single-blind studyIn a typical single-blind study, half of those given the real drug are told they are being given a placebo, half of those given a placebo are told they are being given the real drug, while the other halves are told what they are really being given
13In a single blind study, participants are randomly given the test treatment or placebo, and then followed up with either the test treatment or the placebo
14Double-Blind StudiesResearchers may also have expectations regarding the experiment that may bias the resultsIn this case, the researcher should also not know who is being given the placebo and who is being given the real treatmentA double-blind study is where both the participants and the experimenters are unaware of who is in the control group or experimental groupThe Food and Drug Administration (FDA), which tests the safety of all drugs in the United States, requires that all studies be done as double-blind studies
15A double-blind study is essentially the same as a single-blind study, except that the results are further secured by the experimenter also not knowing if the test or the placebo is being administered
16Central Tendency and Dispersion One of the purposes of research is to be able to generalize and find out what a typical, or average, response isResearchers ascertain the central tendency (the general area where responses tend to be)The most common measures of central tendency are mean, median, and modeThe mean is the average, the median is the middle number when the numbers are put from highest to lowest, and the mode is the number that occurs most oftenResearchers are also interested how spread out the data is, and use the range and standard deviation to measure thisThe range is simply the smallest number subtracted from the largest numberThe standard deviation measures how far each item of data is from the mean
17Mean Median and Mode, along with Range, tell us about the Central Tendency, or what a typical number/ answer is